The kinetics of gelation of deoxyhemoglobin S is being studied using rheological techniques. A magnetic microrheometer has been modified to give the time course of both the lag and the gelation phases of the gelling reaction, using a rapid temperature jump to initiate the reaction. The instrument gives changes in both the viscous and elastic character of the sample with time. Gelation kinetics and parameters for both lag and gelation phases will be obtained as a function of hemoglobin concentration, temperature, pO2, and other variables.